Well construction and completion

ABSTRACT

A well sealing system includes a tailipipe set in a wellbore casing, the annular space between the tailpipe and the casing being sealed by a packer comprising at least two annular seals, and the internal diameter of the tailpipe being sealed by at least two internal seals. Disclosed are also an apparatus and a method for providing a casing in a bore hole for a well an offshore location, comprising the steps of: a) fabricating a casing in a location remote from the offshore well location; b) floating the casing to the location; c) orienting the casing to a substantially vertical position; d) lowering in a drilling assembly; e) operating a drill bit included in the drilling assembly to drill a borehole; f) lowering the casing into the bore hole as required.

This invention is a new method of constructing a well in deepwater without the use of a rig

Setting up a rig when drilling a subsea well is an expensive and time-consuming exercise. Casing sections are transported to an offshore rig, and as the bore hole is extended a new casing section is lowered onto the top of the previous casing and secured to it to extend the casing string. The object of the present invention is to provide a new method of constructing an offshore well without the use of a rig.

According to the present invention, there is provided a well sealing system including a tailipipe set in a wellbore casing, the annular space between the tailpipe and the casing being sealed by a packer comprising at least two annular seals, and the internal diameter of the tailpipe being sealed by at least two internal seals, so that the wellbore above the tailpipe and the wellbore below the tailpipe are separated by two layers of seals.

According to another aspect of the present invention, there is provided a length of casing for installation in a wellbore, the casing including a dynamic seal which seals the annulus between the outer diameter of the length of casing and the inner diameter of any previously installed conductor or casing lengths.

According to a further aspect of the present invention, there is provided a method of providing a casing a bore hole for a well an offshore location, comprising the steps of

-   a) fabricating a casing in a location remote from the offshore well     location -   b) floating the casing to the location -   c) orienting the casing to a substantially vertical position -   d) lowering in a drilling assembly -   e) operating a drill bit included in the drilling assembly to drill     a borehole -   f) lowering the casing into the bore hole as required.

According to another aspect of the present invention, there is provided a casing installation system comprising a casing supported by flotation means, and a first ship for towing the casing, and an orientation means for orienting the casing vertically.

This method of deployment allows the use of a length of casing which may be very much longer than the sections of casing currently employed. This entirely obviates having to short sections of casing together on a rig to produce a casing string.

Other key benefits are;

The casing is manufactured and quality assured in a controlled environment. Independent of drilling process and time line.

Significantly lower cost vessel used to deploy casing, drill and complete the well.

Umbilical supports the casing and supplies the drilling fluid

When cementing casing, umbilical is retracted to deactivate circulation ports used in the drilling process.

The following figures describe one embodiment of the invention

FIG. 1. is a illustration of the method connecting a floating vessel to a section of floating tubing.

FIG. 2. is a illustration of the method for orientating the floated tubing from horizontal to vertical on a floating vessel

FIG. 3 Is a more detailed side view cross section of the casing prepared on land, which has been floated to the vessel.

FIG. 4 is a spreadsheet table of the welded casing properties for each stage

FIG. 5. is a sequence in a typical drilling process

FIG. 6 is a further sequence in the drilling process

FIG. 7 is a further sequence in the drilling process

FIG. 8 is a further sequence in the drilling process

FIG. 9 is a further sequence in the drilling process

FIG. 10 is a further sequence in the drilling process

FIG. 11. is a side view of a well with the welded tubing completion being installed

FIG. 12. is a similar view to FIG. 2 with the well completion at a different stage in the process

FIG. 13. is a similar view to FIG. 2 with the well completion at a different stage in the process

FIG. 14. is a similar view to FIG. 11 this time this is a smart well type of completion

FIG. 15 is a similar view to FIG. 14 with a through tubing electrical submersible pumping system docked and operating.

FIG. 16 Is a plan view of a smart completion tubing requirement

FIG. 17 is a plan view of the empty casing

FIG. 18 is a plan view of the smart well completion shown in FIG. 16 installed inside the casing show in FIG. 17

Referring to FIGS. 1 and 2, a length of well bore tubing 1 welded together onshore is towed out to the drill site by a towing vessel (not shown). The tubing is be supported by bouys 2 distributed along its length, each buoy having a releasable clamping mechanism holding it to the casing. The releasable clamping mechanism may be activated by a number of means to release it from the tubing as it is pulled onto the deployment vessel 3. The deployment vessel picks up a line (not shown) on the tubing to enable it to pull it to the vessel. The tubing is then connected to a “snake” 4 i.e. a flexible member preinstalled in the pulling device 5, which is used to pick up the tubing from the water and feed it into the injector 5 situated over the moon pool. Once the snake had passed through the injector it is removed and hung off in the moon pool as shown at 7, and the rest of the tubing is then pulled on board and deployed through the moonpool. As each buoy approaches the vessel, the clamping mechanism is activated to release it from the tubing. The buoys are then be stored on the vessel deck area 8.

Ideally, two vessels are involved in the deployment of the casing string—a towing vessel which tows the casing string to the drill site, and a deployment vessel which takes the casing string from the towing vessel and manoeuvres the casing string to the seabed. The two vessels may support the casing together while the casing string is being oriented. Alternatively, a single vessel may both tow the casing to the drill site, and orient and deploy the casing string.

The casing may be fabricated on-shore so that it is already fully prepared for deploying into the well, or final procedures for readying the casing may be carried out immediately before the casing is deployed. Referring to FIG. 3, an internal circulating tube 30 is installed in the casing, and upper and lower terminations 31 and 32 are positioned at each end of the casing. This enables the drilling bottom hole assembly (BHA) to be directly connected to a connector 33 on the lower termination 31, while the conveyance tubing can be connected to the connector 34 on the upper termination 32. The circulation paths will be explained below and in the following figures.

FIG. 4 shows a spreadsheet with typical well geometries, and the maximum casing lengths if the conveyance means was 5″ coiled tubing.

Referring to FIGS. 5 to 10 the casing 10 being drilled into the earth is lowered upon an deployment tube 11. The deployment tube is attached to an upper termination 31, where is makes a fluid connection with the internal circulating tube 30. The internal circulating tube 30 also penetrates a lower termination 32 so that fluid can pass out of the internal circulating tube through the lower termination. A seal 40 prevents the upper open hole 41 being subjected to pressure from above the seal. The drilling assembly is situated at the bottom of the casing and is attached via connection 33. Drilling fluid is circulated from surface through the inner tube 11, coming out off the expandable bit 13 and reentering the casing through ports 14, so that cuttings and return fluid flow back to surface of the borehole via the annular space 15. FIG. 5 shows a casing string being installed beneath an already installed conductor section, though the principle described here applies to the conductor section itself and to subsequent casings.

When the casing has reached its maximum depth, collets 42 in uppermost end of the casing locate and support the weight of the casing in a profile 43 of the previous casing or conductor section. The collets also include a sealing surface to seal the casing against the inner surface of the previously installed casing. A ball may be allowed to fall through the tubing to activate the release of both the upper and lower casing termination 32 and 33. Also, cessation of fluid pumping causes the expandable bit to retract to its minimum diameter, so that the inner assembly and bit may then be conveyed back to surface on the inner tube 11.

Referring to FIG. 7, after the drilling BHA has been removed, a cementing string is lowered into the casing, consisting of a length of coiled tubing on which is suspended a dockable and drillable dual non return valve 44. The dual non return valve is positioned immediately above the drilling circulation ports 44. At the upper end of the casing, circulation ports 46 remain exposed to the open bore. Sealing material such as cement 48 is pumped down the coiled tubing, filling the annulus between the borehole sides and the newly installed casing, displaced fluid escaping through the circulation ports 46, until sufficient sealing material has been delivered to the annulus.

Once the cement is set, a new casing string 21 is lowered on a tube 52 into the well with the drilling BHA 22 installed inside it. As for the previous casing string, the casing string 21 has a stepped seal 50 which prevents pressure during the drilling process being exerted on the upper section of open hole. Once the casing reaches the top of the previous casing, the stepped seal 50 disengages from the casing 25 and engages with the top of the previously installed casing 10, supplementing the sealing portions of the previously installing casing's collets 42 as an additional seal. The casing 25 includes a secondary annular seal 51 having a smaller radius, which seals the casing 25 against the inner surface of the previously installed casing 25. Surface pressure control hardware 23 is deployed at the same time and docks onto the wellhead 24. The fluid circulation path is down the central tube 11 and internal circulating tube 30, through the bit, through the tubing ports 14 and up the annulus between internal circulating tube 30 and the casing 21, and back to the surface vessel 3 via the umbilical 26

Alternatively to providing the drilling assembly connected to the end of the casing, a drilling assembly may be deployed separately and inserted through the casing.

FIGS. 11 to 13, show a typical wellbore completion, with welded tubing 101 fully deployed in the well. The lower end of the welded tubing is attached via a releasable mechanism 110 to a lower tailpipe assembly which consists of a double packer 111 and tubing conveyed perforating guns 112. At the upper end a conventional tubing hanger 113 allows the welded tubing 101 to be hung in the wellhead 114. The completion is deployed from the vessel suspended on tubing 115, and once the completion has landed the tubing is released from the hanger 113 by conventional means, and is then pulled back to the vessel by the injector 5, and re-laid back onto the ocean, to be used again as required.

Referring to FIG. 12, the perforating guns 112 are fired to create perforations 116 through which well bore fluids are produced.

At some point, it maybe necessary to remove the completion from the well. To do this, two barriers are required to protect the surface from the reservoir. Referring to FIG. 13, the tailpipe already has a dual packer 111 providing two annular barriers, so two internal plugs 117 are deployed through tubing and set in the tailpipe. These internal plugs may mate with a profile on the inner diameter of the tailpipe to be secured in place to plug the well bore. There is now a double seal on both the internal and external diameter of the tailpipe between the former oil-producing part of the wellbore and the wellbore above this, so the completion can then be removed and replaced as required, or the well may be abandoned if it has come to the end of its useful life.

Referring to FIG. 14 to 18, there is shown a more sophisticated “smart” type completion. The key difference here is there are many cables 120 and control lines 121 attached by clamps 124 and 125 which are welded to the outside of the welded tubing 101. As the structure is assembled onshore, the cable protector 122 can be welded to the outside of the tubing 101, and can either be continuous or nearly continuous so providing the ultimate protection to the cables and control lines attached to its outside. In addition, all these control lines can be fully function tested and quality assured prior to being towed out to the well site, saving many days of previously expensive rig time. In addition, to enable to tubing to be stripped through BOPs on the wellhead, the whole of the outer surface could be encapsulated 123 with a suitable polymer to provide a smooth round exterior. FIG. 16 shows the assembly as it would be prior to being installed in the well, and FIG. 18 shows the assemble as it would be installed in the well.

Referring in particular to FIGS. 14 and 15, the power cable 120 in this example would power a downhole electric submersible pump 130, deployed on a slickline 132 and powered by a down hole wet connect 131, the details of such a deployment and possible retrieval are described in WO 2005 003506. 

1. A well sealing system including a tailpipe set in a wellbore casing, the annular space between the tailpipe and the casing being sealed by a packer comprising at least two annular seals, and the internal diameter of the tailpipe being sealed by at least two internal seals, so that the wellbore above the tailpipe and the wellbore below the tailpipe are separated by two layers of seals.
 2. A well sealing system according to claim 1 wherein tubing extends from the surface of the wellbore to the tailpipe, and the two internal seals are deployed down this tubing.
 3. A well sealing system according to claim 1 wherein the two internal seals engage with a profile in the internal diameter of the tailpipe.
 4. A well sealing system according to claim 2, wherein the tubing is disengaged after the internal seals have been deployed.
 5. A well sealing system according to claim 1 wherein the internal seals are removable.
 6. A length of casing for installation in a wellbore, the casing including a dynamic seal which seals the annulus between the outer diameter of the length of casing and the inner diameter of any previously installed conductor or casing lengths.
 7. A length of casing according to claim 6, wherein the dynamic seal includes a disengagable part that can release from the length of casing for installation to engage with the annulus between two previously installed casing lengths.
 8. A length of casing according to claim 7, wherein the dynamic seal includes a non-disengagable part that remains on the length of casing being lowered after the disengagable part has been released, the non-disengagable part continuing to seal the annulus between the length of casing being lowered and a previously installed casing length.
 9. A method of providing a casing a bore hole for a well an offshore location, comprising the steps of a) fabricating a casing in a location remote from the offshore well location b) floating the casing to the location c) orienting the casing to a substantially vertical position d) lowering in a drilling assembly e) operating a drill bit included in the drilling assembly to drill a borehole f) lowering the casing into the bore hole as required.
 10. A method according to claim 9 wherein the drilling assembly is lowered simultaneously with the casing.
 11. A method according to claim 9 wherein a bore hole pressure control means is lowered onto the bore hole after the casing is introduced to the bore hole.
 12. A method according to claim 9 wherein an umbilical having a flowpath is included in fluid communication with the bore hole.
 13. A method according to claim 9 wherein after the casing is lowered in the bore hole to its final position, a cement plug is formed at the bottom of the casing before the drilling assembly is removed from the bore hole.
 14. A method according to claim 9 wherein a subsequent casing is provided at the sea bed in the same manner, the subsequent casing having an outer diameter smaller than that of the inner diameter of the previous said casing, the subsequent casing being lowered through the previous casing.
 15. A casing installation system comprising a casing supported by flotation means, and a first ship for towing the casing, and an orientation means for orienting the casing vertically.
 16. A casing installation system according to claim 15 wherein the casing is supported between a first ship and a second ship during orientation.
 17. A casing installation system according to claim 16 wherein a control system including one or more rotatable grips are attached to the casing to hold the casing while it is orientated.
 18. A casing installation system according to claim 15 wherein a drilling assembly is provided that is insertable within the casing.
 19. A casing installation system according to claim 15 wherein a sealing means is provided for sealing the bore hole from the surrounding environment. 